Method and device for locating the position, on the right or on the left, of a wheel of a vehicle

ABSTRACT

A method and device for locating the position, on the right or on the left, of a vehicle wheel. The wheel is equipped with two magnetic sensors having axes of maximum sensitivity lying in a plane that is secant to the axis of rotation of the wheel and which are offset from one another in this secant plane by a predetermined angle θ. As the vehicle moves in a given travel direction, a signal generated by the variation in a magnetic field is measured at the terminals of each of the magnetic sensors to deliver two periodic signals phase-shifted from one another by an angular value equal to (+or −) θ, this phase shift is used to determine the direction of wheel rotation, and from such direction and the travel direction, the location, on the right or on the left, of the wheel is deduced.

The invention relates to a method and a device for locating theposition, on the right or on the left, of a wheel of a vehicle.

Motor vehicles are increasingly possessing, for safety purposes,monitoring systems comprising sensors mounted on each of the wheels ofthe vehicle, these sensors being dedicated to measuring parameters, suchas the pressures or temperatures of the tires with which these wheelsare equipped, and intended to inform the driver of any abnormalvariation in the parameter measured.

These monitoring systems are conventionally provided with a sensormounted on each of the wheels of the vehicle and comprising amicroprocessor and a radiofrequency emitter (or RF emitter) and with acentral unit for receiving the signals emitted by the emitters,comprising a computer incorporating a radiofrequency receiver (or RFreceiver) connected to an antenna.

One of the problems that such monitoring systems need to solve lies inthe need to associate with each signal received by the receiver of thecentral unit, an information item regarding the location of the sensorand therefore of the wheel from which this signal originated, this needpersisting throughout the life of the vehicle, that is to say having tobe observed even when the wheels have been changed or simply when theposition of these wheels has been swapped around.

At the present time, a first location method is to use threelow-frequency antennas each one positioned near one of the wheels of thevehicle and to perform a location procedure that consists insuccessively energizing each of these three antennas by emitting alow-frequency magnetic field. Each of these sensors then (in turn)discloses its identification number to the central unit. The latterassociates this identification number with a position on the vehicle(front right, front left, rear right, rear left).

According to this procedure, the sensor mounted on the wheel locatednear the energized antenna, in response to and bound for the centralunit causes the emission of a low-frequency signal containing anidentification code identifying said sensor so that the successiveenergizing of the three antennas leads to the location of the threesensors mounted on the wheels adjacent to these antennas and, bydeduction, leads to the location of the fourth sensor.

The main advantage with such a method lies in the fact that the locationprocedure is very quick and leads to almost instantaneous location afterthe vehicle has been started.

By contrast, this solution entails equipping the vehicle with threeantennas and all the related requisites: connecting cables, controlamplifiers, etc., which means that it proves expensive.

In order to limit the cost required by the location procedure, a secondsolution currently implemented consists first of all in reducing thenumber of antennas to two and in positioning these two antennas near thetwo front wheels, so as to allow said two front wheels to be located,and so as to allow the latter to be differentiated from the two rearwheels.

This second solution also combines with the use of the two antennas atechnique based on a statistical method that consists in comparing theaccelerations of the wheels in a bend in order to discriminate betweenthe left wheels and the right wheels.

Because one antenna has been eliminated, this second solution proves, asmentioned above, less expensive than the first solution described.However, this saving is made at the expense of the speed of the locationprocedure which, in this second solution, proves to be relativelylengthy because a significant amount of running time is required inorder to discriminate between left and right.

The present invention is aimed at alleviating the disadvantageassociated with the length of the right/left location procedure of thesecond technique described hereinabove and its main objective is toprovide a right/left location procedure that is very efficient in termsof responsiveness and in addition, to implement it, requires hardwarethe overall cost of sourcing and fitting of which is lower than theoverall cost of an antenna.

To this end, the invention is aimed firstly at a method for locating theposition, on the right or on the left, of a wheel of a vehicle, whereby:

-   -   said wheel is equipped with two magnetic sensors having axes of        maximum sensitivity lying in a plane that is secant to the axis        of rotation of the wheel and are offset from one another, in        this secant plane, by a predetermined angle θ,    -   and, as the vehicle moves in a given direction of travel:    -   a signal generated by the variation in the magnetic field is        measured at the terminals of each of the two magnetic sensors so        as to deliver two periodic signals phase-shifted with respect to        one another by an angular value equal to (+ or −) θ, each one        representative of the variations in the values of the magnetic        field as detected by said magnetic sensors during one revolution        of the wheel,    -   this phase shift is used to determine the direction of rotation        of the wheel,    -   and from this direction of rotation and from the direction of        travel of the vehicle, the location of the wheel, whether        positioned on the right or on the left, is deduced.

The principle underlying the invention has therefore been to equip eachwheel to be located of a vehicle with two magnetic sensors arranged insuch a way that the signals at the terminals of said sensors are phaseshifted from one another and to deduce from this phase shift thedirection of rotation and the location, on the right/on the left, of thewheel.

According to this principle, the invention leads to very quick locationof the position, on the right/on the left, of a wheel, which location isin fact obtained after a few revolutions of the wheel. In addition, theoverall cost (sourcing and fitting) of two magnetic sensors is lowerthan that of one antenna.

It should be noted that it is known practice, particularly frominternational patent application WO2004/048131, to perform right/leftlocation of a wheel by equipping the latter with two accelerometersarranged in such a way that the vertical components of the directions ofmeasurement of said accelerometers are offset by an angular value Δ andthat the signals delivered by these accelerometers are phase shifted bythis same value Δ.

Such a method therefore displays certain analogies with the method ofthe invention because it consists in determining the direction ofrotation of the wheel by analyzing the phase shift between the signalsdelivered by two sensors mounted on the wheel.

However, according to that anterior document, the sensors used consistof accelerometers, that is to say, on the one hand, of sensors that havea high cost price and, on the other hand, of measurement means theresults of the measurements of which can be used only when the vehicleis moving along at a speed above a given threshold of the order of 40km/h.

For its part, the invention consists in using two very low-pricesensors, the results of the measurements of which can be used veryquickly right from the first few revolutions of the wheel of thevehicle.

In order to obtain two readily discriminatable signals, and according toan advantageous implementation of the invention, the two magneticsensors are positioned in such a way that their axes of maximumsensitivity lie orthogonal to one another.

To the same end and advantageously according to the invention, the twomagnetic sensors are positioned in such a way that their axes of maximumsensitivity lie in a plane orthogonal to the axis of rotation of thewheel.

Furthermore, with a view to increasing the sensitivity of the methodaccording to the invention and advantageously, the cyclic signalrepresentative of the variations in the values of the magnetic field asdetected by each magnetic sensor is amplified and shaped in such a wayas to obtain a periodic signal of squarewave shape as the vehicle movesalong.

With the same view of increasing the sensitivity and therefore thereliability of the method according to the invention, the vehicle isadvantageously equipped with a magnet that is fixed with respect to eachwheel equipped with two magnetic sensors, said magnet being positionedand having a power suitable for generating a magnetic field covering azone through which said magnetic sensor passes as said wheel rotates.

The invention extends to a device for locating the position, on theright or on the left, of a wheel of a vehicle, comprising, mounted onsaid wheel:

-   -   two magnetic sensors having axes of maximum sensitivity lying in        a plane that is secant to the axis of rotation of the wheel and        which are offset from one another in this secant plane by a        predetermined angle θ,    -   means for measuring a signal at the terminals of each of the        magnetic sensors, these means being able to deliver two periodic        signals phase-shifted from one another by an angular value equal        to (+or −) θ, each representative of the variations in the        values of the magnetic field as detected by said magnetic        sensors during a revolution of the wheel,    -   and a calculation unit programmed to determine, from the phase        shift between the two periodic signals, the direction of        rotation of the wheel and, from this direction of rotation and        from the direction of travel of the vehicle, to deduce the        location, on the right or on the left, of the wheel.

Advantageously according to the invention, the two magnetic sensors arepositioned in such a way that their axes of maximum sensitivity lie in aplane orthogonal to the axis of rotation of the wheel.

In addition, these two magnetic sensors are advantageously positioned insuch a way that their axes of maximum sensitivity lie orthogonal to oneanother.

Furthermore, advantageously according to the invention, the measurementmeans comprise means for amplifying and means for shaping the amplifiedsignal which are able to convert it into a periodic signal of squarewaveform.

The location device according to the invention comprises, alsoadvantageously, a magnet mounted fixedly on the vehicle with respect toeach wheel equipped with two magnetic sensors, said magnet beingpositioned and having a power suitable for generating a magnetic fieldcovering a zone through which said magnetic sensors pass as said wheelrotates.

Other characteristics, objects and advantages of the invention willbecome apparent from the detailed description which follows withreference to the attached drawings which by way of nonlimiting examplesillustrate one preferred embodiment thereof. In these drawings:

FIG. 1 is a partial and schematic perspective view of a vehicle equippedwith a location device according to the invention,

FIG. 1 a is a detailed diagram depicting the relative arrangement of thetwo magnetic sensors of the location device according to the invention,

FIG. 2 is a functional block diagram of the processing electronics ofthis location device, and

FIGS. 3 a and 3 b are two diagrams illustrating the principle of thelocation method employed according to the invention.

The location device according to the invention depicted by way ofexample in FIG. 1 is intended to locate the position, on the right or onthe left, of a wheel of a vehicle.

This location device is more specifically intended to be installed onvehicles equipped with a monitoring system comprising electronic units 1mounted on each of the wheels 2 of the vehicles 3, incorporating sensorsdedicated to measuring parameters such as the pressure and/or thetemperature of the tires with which these wheels 2 are equipped, andintended to inform the driver of any abnormal variation in the parametermeasured.

This location device firstly comprises two magnetic sensors 4, 5designed to be able to be incorporated into the same electronic unit 1and arranged in such a way that their respective axes of maximumsensitivity S4, S5 lie in the same plane perpendicular to the axis ofrotation of the wheel 2 and are offset from one another by apredetermined angle θ=90°. To this end, and according to the exemplaryembodiment depicted in the figures, these two magnetic sensors 4, 5, onthe one hand, are aligned along the same radial axis with respect withrespect to the axis of rotation R of the wheel 2 and, on the other hand,consist in:

-   -   a coil 4 comprising a soft iron core, positioned such that the        longitudinal axis of said core, that forms the axis of maximum        sensitivity S4 of said coil, coincides with an axis tangential        to a circle centered on the axis of rotation R of the wheel 2,    -   and a flat coil 5 formed of a flat winding positioned in such a        way that the longitudinal axis of said winding that forms the        axis of maximum sensitivity S5 of said coil, coincides with the        aforementioned radial axis.

Positioned in this way, as the wheel 2 rotates, each of these coils 4, 5exhibits, between its two terminals, a potential difference that variesaccording to a sinusoidal function with a period equal to the period ofrotation of said wheel.

A magnetic sensor 4, 5 mounted on a wheel 2 of a vehicle 3 in effectdetects the overall magnetic field obtaining around this sensor, thisoverall magnetic field being made up of the earth's magnetic field towhich the environmental magnetic field that may in particular resultfrom the presence of electrical or magnetic equipment on board thevehicle is added.

Now, as the wheel 2 rotates, this magnetic sensor 4, 5 moves in acircular path so that this sensor 4, 5 detects a variable magnetic fieldand the potential difference measured at the terminals of said sensorexhibits corresponding cyclic variations.

Furthermore, since according to the invention the two coils 4, 5 arepositioned in such a way that their axes of maximum sensitivity S4, S5are orthogonal, the signals representative of the potential differenceat the terminals of said coils are phase shifted from one another by anangle equal to (+or −) 90° so that, as depicted in FIGS. 3 a and 3 b,analyzing this phase shift makes it possible to determine the directionof rotation of the wheel 2.

With a view to measuring and processing the potential difference at theterminals of each coil 4, 5, the device according to the inventionfirstly comprises an amplification module 7 and a shaping module 8incorporating a comparator, so that as the wheel 2 rotates:

-   -   the signal at the terminals of each coil 4, 5 is a sinusoidal        signal of very low amplitude,    -   the signal leaving the amplification module 7 is a sinusoidal        signal with the same period as the previous signal but an        amplitude greater than that of said signal,    -   and the signal leaving the shaping module 8 is a squarewave        signal of the same period as the sinusoidal signals.

The device according to the invention further comprises a calculationunit 9 to which the shaped signal is delivered and programmed to:

-   -   determine, as stated above, from analyzing the phase shift        between the two sinusoidal signals, the direction of rotation of        the wheel 2,    -   and from this direction of rotation and from the direction of        travel of the vehicle 3, determined elsewhere by any method        known per se, deduce the position, on the right or on the left,        of the wheel 2.

Lastly, and according to the invention, the vehicle 3 may also comprise,as depicted in FIG. 1, permanent magnets or electromagnetic magnets 10fixed to the carbody at the wheel arches 11 so that the magnetic fieldcreated by each of these magnets 10 is detected by the magnetic sensors4, 5 mounted on the corresponding wheel 2, increasing the overallmagnetic field detected by said sensors and therefore the amplitude ofthe sinusoidal signals leaving the amplification module 7.

The device according to the invention described hereinabove therefore,by incorporating two simple low-cost magnetic sensors 4, 5 into eachelectronic unit 1 on board a wheel 2 of a vehicle 3, makes it possiblevery quickly, after a few revolutions of the wheel 2, to locate theposition, on the right or on the left, of said wheel.

1. A method for locating the position, on the right or on the left, of awheel (2) of a vehicle (3), characterized in that it consists: inequipping said wheel with two magnetic sensors (4, 5) having axes ofmaximum sensitivity (S4, S5) lying in a plane that is secant to the axisof rotation (R) of the wheel (2) and which are offset from one anotherin this secant plane by a predetermined angle θ, and, as the vehiclemoves in a given direction of travel: in measuring a signal generated bythe variation in a magnetic field at the terminals of each of themagnetic sensors (4, 5) so as to deliver two periodic signalsphase-shifted with respect to one another by an angular value equal to(+or −) θ, each one representative of the variations in the values ofthe magnetic field as detected by said magnetic sensors during onerevolution of the wheel (2), in determining from this phase shift thedirection of rotation of the wheel (2), and in deducing from thisdirection of rotation and from the direction of travel of the vehicle(3), the location of the wheel (2), whether positioned on the right oron the left.
 2. The location method as claimed in claim 1, characterizedin that the two magnetic sensors (4, 5) are positioned in such a waythat their axes of maximum sensitivity (S4, S5) lie in a planeorthogonal to the axis of rotation (R) of the wheel (2).
 3. The locationmethod as claimed in claim 2, characterized in that the two magneticsensors (4, 5) are positioned in such a way that their axes of maximumsensitivity (S4, S5) lie orthogonal to one another.
 4. The locationmethod as claimed in claim 1, characterized in that the vehicle (3) isequipped with a magnet (10) that is fixed with respect to each wheel (2)equipped with two magnetic sensors (4, 5), said magnet being positionedand having a power suitable for generating a magnetic field covering azone through which said magnetic sensors pass as said wheel rotates. 5.A device for locating the position, on the right or on the left, of awheel (2) of a vehicle (3), characterized in that it comprises, mountedon said wheel: two magnetic sensors (4, 5) having axes of maximumsensitivity (S4, S5) lying in a plane that is secant to the axis ofrotation (R) of the wheel (2) and which are offset from one another inthis secant plane by a predetermined angle θ, means (7, 8) for measuringa signal at the terminals of each of the magnetic sensors (4, 5), thesemeans being able to deliver two periodic signals phase-shifted from oneanother by an angular value equal to (+or −) θ, each representative ofthe variations in the values of the magnetic field as detected by saidmagnetic sensors during a revolution of the wheel (2), and a calculationunit (9) programmed to determine, from the phase shift between the twoperiodic signals, the direction of rotation of the wheel (2) and, fromthis direction of rotation and from the direction of travel of thevehicle (3), to deduce the location, on the right or on the left, of thewheel (2).
 6. The location device as claimed in claim 5, characterizedin that the two magnetic sensors (4, 5) are positioned in such a waythat their axes of maximum sensitivity (S4, S5) lie in a planeorthogonal to the axis of rotation (R) of the wheel (2).
 7. The locationdevice as claimed in claim 6, characterized in that the two magneticsensors (4, 5) are positioned in such a way that their axes of maximumsensitivity (S4, S5) lie orthogonal to one another.
 8. The locationdevice as claimed in claim 6, characterized in that it comprises amagnet (10) mounted fixedly on the vehicle (3) with respect to eachwheel (2) equipped with two magnetic sensors (4, 5), said magnet beingpositioned and having a power suitable for generating a magnetic fieldcovering a zone through which said magnetic sensors pass as said wheelrotates.
 9. The location device as claimed in claim 7, characterized inthat it comprises a magnet (10) mounted fixedly on the vehicle (3) withrespect to each wheel (2) equipped with two magnetic sensors (4, 5),said magnet being positioned and having a power suitable for generatinga magnetic field covering a zone through which said magnetic sensorspass as said wheel rotates.
 10. The location method as claimed in claim2, characterized in that the vehicle (3) is equipped with a magnet (10)that is fixed with respect to each wheel (2) equipped with two magneticsensors (4, 5), said magnet being positioned and having a power suitablefor generating a magnetic field covering a zone through which saidmagnetic sensors pass as said wheel rotates.
 11. The location method asclaimed in claim 3, characterized in that the vehicle (3) is equippedwith a magnet (10) that is fixed with respect to each wheel (2) equippedwith two magnetic sensors (4, 5), said magnet being positioned andhaving a power suitable for generating a magnetic field covering a zonethrough which said magnetic sensors pass as said wheel rotates.